1. Field of the Invention
The present invention relates generally to communication systems for wellsite operations. More specifically, the present invention relates to wellbore communication systems for passing signals between a surface unit and rig with a downhole tool suspended in a wellbore via a drill string.
2. Background of the Related Art
The harvesting of hydrocarbons from subterranean formations involves the drilling of wellbores into the earth. To create the wellbore, a downhole drilling tool is suspended from a drilling rig and advanced into the earth via a drill string. As the drilling tool is advanced, a drilling mud is pumped from a surface mud pit, through the drilling tool and out the drill bit to cool the drilling tool and carry away cuttings. The fluid exits the drill bit and flows back up to the surface for recirculation through the tool. The drilling mud is also used to form a mudcake to line the wellbore.
During the drilling operation, it is desirable to provide communication between the surface equipment and the downhole tool. Telemetry devices are typically incorporated into downhole tools to allow, for example, power, command and/or communication signals to pass between a surface unit and the downhole tool. These signals are used to control and/or power the operation of the downhole tool and send downhole information to the surface.
FIG. 1 illustrates a prior art wellsite system used during drilling operations. The wellsite system includes a surface system 2 of the prior art, a downhole system 3 of the prior art, and a surface control unit 4 of the prior art. In the illustrated embodiment, a borehole 11 is formed by rotary drilling in a manner that is well known. Those of ordinary skill in the art given the benefit of this disclosure will appreciate, however, that the present invention also finds application in drilling applications other than conventional rotary drilling (e.g., mud-motor based directional drilling), and is not limited to land-based rigs.
The downhole system 3 includes a drill string 12 suspended within the borehole 11 with a drill bit 15 at its lower end. The surface system 2 includes the land-based platform and derrick assembly 10 positioned over the borehole 11 penetrating a subsurface formation F. The assembly 10 includes a rotary table 16, kelly 17, hook 18 and rotary swivel 19. The drill string 12 is rotated by the rotary table 16, energized by means not shown, which engages the kelly 17 at the upper end of the drill string. The drill string 12 is suspended from a hook 18, attached to a traveling block (also not shown), through the kelly 17 and a rotary swivel 19, which permits rotation of the drill string relative to the hook.
The surface system further includes drilling fluid or mud 26 stored in a pit 27 formed at the well site. A pump 29 delivers the drilling fluid 26 to the interior of the drill string 12 via a port in the swivel 19, inducing the drilling fluid to flow downwardly through the drill string 12 as indicated by the directional arrow 9. The drilling fluid exits the drill string 12 via ports in the drill bit 15, and then circulates upwardly through the region between the outside of the drill string and the wall of the borehole, called the annulus, as indicated by the directional arrows 32. In this manner, the drilling fluid lubricates the drill bit 15 and carries formation cuttings up to the surface as it is returned to the pit 27 for recirculation.
The drill string 12 further includes a bottom hole assembly (BHA), generally referred to as 40, near the drill bit 15 (in other words, within several drill collar lengths from the drill bit). The bottom hole assembly includes capabilities for measuring, processing, and storing information, as well as communicating with the surface. The BHA 40 thus includes, among other things, an apparatus 41 for determining and communicating one or more properties of the formation F surrounding borehole 11, such as formation resistivity (or conductivity), natural radiation, density (gamma ray or neutron), and pore pressure.
The BHA 40 further includes drill collars 42, 43 for performing various other measurement functions. Drill collar 43 houses a measurement-while-drilling (MWD) tool. The MWD tool further includes an apparatus 45 for generating electrical power to the downhole system. While a mud pulse system is depicted with a generator powered by the flow of the drilling fluid 26 that flows through the drill string 12 and the MWD drill collar 43, other power and/or battery systems may be employed.
Sensors are located about the wellsite to collect data, preferably in real time, concerning the operation of the wellsite, as well as conditions at the wellsite. Surface sensors or gauges 5, 6, 7 are disposed about the surface systems to provide information about the surface unit, such as standpipe pressure, hookload, depth, surface torque, and rotary rpm among others. Sensor 5 is preferably adapted to receive data from downhole sensor 8. Downhole sensors or gauges 8 are disposed about the drilling tool and/or wellbore to provide information about downhole conditions, such as wellbore pressure, weight on bit, torque on bit, direction, inclination, collar rpm, tool temperature, annular temperature and tool face, among others. The information collected by the sensors and cameras is conveyed to the surface system, the downhole system and/or the surface control unit.
The surface sensors connect to surface unit 4 (of the prior art, as shown in FIG. 1) where the signal data received from the downhole sensors is processed and put into a format the clients to review. The surface sensor 5, 6 and 7 are connected to the surface unit 4 via a junction box 70. The junction box is a means to combine the multiple wires or cables 64, 68, 69 from the surface sensors 5, 6 and 7, respectively into one large cable 74. In this junction box, the input wires can be spliced together such that the junction box reduces the number of wires that extend from the box and connect to the surface unit 4. Cable 74 provides the hard-wired communication between the junction box 70 and the surface unit 4.
The surface unit 4 contains various processing equipment for processing the signals that are transmitted from the surface sensors. Analog signals from the surface sensors are converted to digital values and then processed in the surface unit 4. This processing function results in the generation of displays reflecting the information initially gathered from the downhole sensors.
The MWD tool 43 includes a communication subassembly 44 that communicates with the surface unit 4. The communication subassembly 44 is adapted to send signals to and receive signals from the surface using mud pulse telemetry. The communication subassembly may include, for example, a transmitter that generates a signal, such as an acoustic or electromagnetic signal, which is representative of the measured drilling parameters. The generated signal is received at the surface by transducers, represented by reference numeral 31, that convert the received acoustical signals to electronic signals for further processing, storage, encryption and use according to conventional methods and systems. Communication between the downhole and surface systems is depicted as being mud pulse telemetry, such as the one described in U.S. Pat. No. 5,517,464, assigned to the assignee of the present invention. It will be appreciated by one of skill in the art that a variety of telemetry systems may be employed, such as wired drill pipe, electromagnetic, acoustic, seismic or other known telemetry systems.
The surface unit 4 is typically operatively connected to the surface system 2 and the downhole system 3 of the wellsite for communication therewith. A monitor (not shown) is typically provided at the surface unit and manned by an operator. The operator may send commands from the surface unit to the downhole tool. The operator may also monitor downhole operations by viewing data displayed on the monitor of the surface unit.
As shown in FIG. 1, data generated by the surface and downhole systems is transferred to the surface unit 4 individually via a set of hard-wired cables. The first set of wired connections 64, 68, 49 are ‘rigged-up’ to transfer measurements from sensors about the wellsite to a junction box 70. A second hard-wired connection 74 is necessary to transfer the measurements from the junction box 70 to the surface unit 4.
The hard-wired connections typically require the use of numerous physical wires that connect the surface sensors to the surface unit 4 via a junction box 70. Current rig display and sensor acquisition systems are often bulky, heavy and difficult to rig up and down. These sensors 5, 6 and 7 are positioned at various locations at the wellsite. It can be a substantial requirement of time and effort to connect the wiring between the surface unit 4 and the surface sensors 5, 6 and 7. This time typically adds to the expense of the drilling operations. In addition, the bundles of wires at the wellsite can interfere with wellsite operations.
Despite previous advances in data transfer systems, there remains a need to provide techniques for efficient and effective transfer of data from the downhole tool to a surface computer. It is desirable that such a system provides a flexible and efficient means for transferring data from the surface and/or downhole system to a surface computer. It is further desirable to develop a wireless network architecture adaptable to harsh wellsite conditions. Such a system would preferably provide one or more of the following, among others: real-time communications, integrated communication links and/or hardware, simplified hardware configurations, reduced ‘rig up’ time, efficient setup, wired and/or wireless communications and operation, flexible setups, portability to desired locations about the website, reduction of wire lengths, reduced noise and efficient hardware set up.